Basicly the meat and potatoes of it is your chip is going to run like a normal 3ghz p4 until you have two seperate programs running at once, then hyperthreading will allow you to run both at the same time and take up half the amount of time it normally would to complete both.

hyperthreading helps both with using multiple programs at once or when using a program written in a way to properly use the hyperthreading. according to lab tests hyperthreading is very useful with programs that really utilize it very good performance increases, but of course how much of this would you actually notice is hard to say.